Ignition system



Nov. 23, 1965 K. B. BAYS ETAL 3,219,876

IGNITION SYSTEM Filed Sept. 21, 1961 fln LYNN A. ROCKWELL BY GARWMWL THEIR ATTORNEY United States Patent 3,219,876 IGNTTION SYSTEM Kenneth B. Bays and Lynn A. Rockwell, Anderson, Ind., assignors to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Sept. 21, 1961, Ser. No. 139,755 1 Claim. (Cl. 315209) This invention relates to ignition systems for internal combustion engines, and more particularly to an ignition system wherein the amount of current flowing through the primary circuit of the ignition system is controlled as a function of the system voltage.

It is well known that the system voltage of a motor vehicle that supplies the ignition system of the internal combustion engine will vary widely under different conditions of operation. Thus, during cranking of the engine with an electric starting motor the system voltage must drop because the battery must supply the heavy cranking motor load and must also supply ignition power. The charged condition of the battery also is a factor on determining what system voltage is available. In addition, when the cranking of an engine is terminated, the system voltage will rise and will rise still further when the engine drives the generator which then supplies the direct current loads of the motor vehicle including the ignition system.

In order to compensate for the drop in system voltage due to the cranking of an engine, it has been common practice in some ignition systems to provide a resistor in the primary circuit of the ignition system which is shorted out during the cranking of the engine. Typical systems of this type are illustrated in the patents to Leece 1,214,555 and to Mallory 1,769,150.

In contrast to the above noted systems of the Leece and Mallory patents, it is an object of this invention to provide an ignition system wherein the current flowing through the primary circuit of the ignition system is controlled as a function of the system voltage. To be more specific, the resistance of the primary circuit of the ignition system is reduced when the system voltage is reduced and this resistance is increased as the system voltage increases above a predetermined value. With the system of this invention, the increase or decrease in resistance of the primary circuit is made without regard as to what causes the increase or decrease in system voltage.

Another object of this invention is to provide an ignition system wherein the primary circuit of the ignition system includes a resistor which is at times short-circuited by a transistor, the conductivity of the tranisstor being controlled in accordance with system voltage.

Still another object of this invention is to provide an ignition system wherein the resistance of the primary circuit of the ignition system is controlled by circuit elements that have no electrical contacts. This system preferably includes a transistor which at times short circuits a resistor in the primary circuit of the ignition system and includes a static sensing device such as a Zener diode for controlling the conductivity of the transistor.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

The single figure drawings is a schematic circuit illustration of an ignition system made in accordance with this invention.

Referring now to the drawing, the reference numeral designates an internal combustion engine having a plurality of spark plugs one of which is designated by reference numeral 12. The engine 10 drives a timing device which in this case includes a breaker cam 14 and this breaker cam operates a breaker lever 16 carrying a breaker contact 18. The breaker contact 18 cooperates with the fixed breaker contact 20 and as the engine rotates the cam 14 causes the breaker contacts 18 and 20 to open and close in a well known manner. The opening and closing of breaker contacts 18 and 20 causes the lead wires 22 and 24 to be connected and disconnected.

The engine 10 also drives a rotor contact 26 which cooperates with the fixed electrodes 28 in a distributor cap 30. The electrodes 28 are connected respectively with the spark plugs 12 by lead wires 32. Only one of the lead wires 32 has been illustrated but it will be apparent to those skilled in the art that there will be as many lead wires 32 and electrodes 28 as there are spark plugs for the engine 10. In this particular instance, there are six electrodes 28 and therefore there will be six spark plugs for the engine 10 and six lead wires 32.

The rotor electrode 26 is connected with the'secondary winding 34 of an ignition coil 36. This connection is made via the lead wire 38. The opposite side of the secondary winding 34 is connected with the lead wire 40 and it is seen that the primary winding 42 of the ignition coil is connected between lead wires 22 and 40. The lead wire 40 is connected with a resistor 44. The opposite side of this resistor is connected'with junction 46. A resistor 48 is connected between junction 46 and a grounded lead wire 50 which forms a common connection for junctions 52, 54, and 56.

The ignition system of this invention includes a first PNP transistor 58 which has an emitter electrode, a base electrode and a collector electrode. The emitter electrode of transistor 58 is connected with junction 46 whereas the collector electrode of transistor 58 is connected with junction 52. The base electrode of transistor 58 is connected with lead wire 60 and a resistor 62 connects the emitter and base electrodes of transistor 58.

A second PNP transistor 64 is provided which has an emitter electrode connected with junction 66. The collector electrode of transistor 64 is connected with the base electrode of transistor 58 via junction 68 and lead wire 60. A resistor 70 is connected between junctions 68 and 54 and another resistor 72 connects the emitter and base electrodes of transistor 64.

The base electrode of transistor 64 is connected with a lead wire 74 and this lead wire is connected to one side of a Zener diode 76. The Zener diode, as is well known to those skilled in the art, breaks down and conducts in a reverse direction when a predetermined voltage is applied thereacross. At other times when the voltage is below the predetermined breakdown voltage, the diode will prevent current flow between its terminals. The opposite side of Zener diode 76 is connected with lead wire 78 and this lead wire is connected to a shiftable slider 88 on the potentiometer resistor 82. One side of the potentiometer resistor 82 is connected with junction 56 and the opposite side of this potentiometer resistor is connected with resistor 84. The resistor 84 is connected with junction 86 and a resistor 88 is connected between junctions 66 and 86. The junction 86 is connected with lead wire 24 at junction 88 and this junction is connected in series with an ignition switch 90. The opposite side of the ignition switch is connected with a junction and this junction is connected to a direct current power source 92 which in this case takes the form of a storage battery. One end of the storage battery is connected through a switch 93 to a starting motor 94 as is conventional practice in motor vehicle electrical systems, and this battery is charged by a generator 91. When the starting motor 94 is energized by the closure of switch 93, the system voltage which appears between junction 95 and ground, of course, will drop. On the other hand, when the engine is started and the switch 93 is opened, the system voltage which appears between junction 95 and ground will rise and will rise even further when the engine is driving the generator 91 to supply charging current to the battery 92 and also power for the ignition system of the engine. It thus is seen that the system voltage appearing between junction 95 and ground will vary widely during dilferent operating conditions of the motor vehicle and engine.

The ignition system of this invention compensates for the widely varying system voltage in a manner to now be described. It can be seen from the circuit diagram that when the ignition switch 90 is closed, the system voltage is impressed between junction 88 and ground and that current will fiow through switch 90, lead wire 24, through the breaker contacts 18 and 20 when they are closed, through primary winding 42, and then through resistors 44 and 48 to ground. Current flow between junction 46 and ground has two alternate paths, depending upon whether or not the transistor 58 is conducting between its emitter and collector electrodes. If transistor 58 is conducting between its emitter and collector electrodes, the resistor 48 will be short-circuited and the resistance of the primary circuit of the ignition system is reduced.

As the breaker contacts 18 and 20 open and close in timed relationship with operation of the engine, the current flow through primary winding 42 is periodically interrupted and this causes a high voltage to be induced in the secondary winding 34 which is applied to a particular spark plug through the lead wire 38, the rotor contact 26, one of the electrodes 28, the lead wire 32 to the spark plug 12.

It can be seen from the drawing that the resistor 84 and the potentiometer resistor 82 are connected so as to sense the system voltage or in other words, the system voltage will be impressed across these resistors which form a voltage divider. It can also be seen that the voltage impressed across the Zener diode 76 will be dependent upon the voltage appearing across the voltage divider network and therefore will be proportional to system voltage. The Zener diode 76 is selected so that it will break down at system voltages which are greater than a predetermined voltage. As an example, the Zener diode maybe arranged to break down at system voltages which are higher than volts. This 10-volt figure is by way of example and not by way of limitation.

It can be seen that the system voltage at which the Zener diode 76 will break down can be adjusted by adjusting the shiftable slider 80 so that more or less voltage is picked off by the voltage dividing network.

Assuming now that the Zener diode 76 will break down when the system voltage appearing between junction 95 and ground exceeds 10 volts and further assuming that this voltage is now above 10 volts, it can be seen that a circuit will be made between junction 86 and junction 56 that includes resistor 88, the emitter-base circuit of transistor 64, the Zener diode 76 and the lower portion of the potentiometer resistor 82. This will establish current fiow in the emitter-base circuit of transistor 64 and therefore will cause a current flow between the emitter and collector electrodes of transistor 64. With current flowing in the emitter-collector circuit of transistor 64, the junction 68 becomes positive with respect to the junction 46. As a result of this, the voltage of the base electrode of transistor 58 becomes positive with respect to the emitter voltage and the transistor'58 is therefore turned off between its emitter and collector. With transistor 58 turned off between emitter and collector, the resistor 48 will not value.

be short-circuited through the emitter-collector path of 7 transistor 58 and the resistor 48 therefore will be in the primary circuit of the ignition system.

Assuming now that the system voltage drops below 10 volts or below the voltage which will break down the Zener diode 76, the transistor 64 will not longer be conductive between emitter and base electrodes and therefore there will be no emitter to collector current in transistor 64. The junction 68 will therefore have a potential that is negative with respect to the potential of junction 46, and therefore will be emitter to base current in transistor 58 from junction 46, through the emitter to base circuit of transistor 58, through lead wire 60 and then through resistor 70 to the grounded lead wire 50. With emitter to base current flow in transistor 58, the transistor turns on fully between its emitter and collector electrodes to therefore short circuit the resistor 48. The

resistance of the primary circuit of the ignition system has now been reduced by the amount of resistance of the resistor 48 since it now is short-circuited.

It can be seen that with the arrangement that has just been described the resistor 48 is short-circuited by the transistor 58 when the voltage drops below a predetermined value and the transistor 58 is rendered substantially non-conductive between its emitter and collector electrode when the system voltage rises above a predetermined It is also pointed out that the part of the system for controlling the conducivity of transistor 58 is completely void of contacts and that the voltage sensing is accomplished by a static device such as the Zener diodes 76.

In the ignition system that has been shown in the drawing, the timing device has been illustrated as a pair of breaker contacts 18 and 20 which control current flow through the primary winding 42 of the ignition coil. It is to be understood that this timing device could take other forms and might, for example, be a transistor having its emitter and collector electrodes connected between lead wires 22 and 24, the transistor then controlling current flow through the primary winding of the ignition coil. The timing device could take other forms without departing from the spirit and scope of this invention.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

An ignition system for an internal combustion engine comprising, terminal means adapted to be connected with a source of system voltage, an ignition coil having a primary winding and a secondary winding, a primary circuit including said primary winding and a resistor, a first transistor having emitter, base and collector electrodes, a second transistor having emitter, base and collector electrodes, means connecting the emitter-collector circuit of said first transistor across said resistor, means for connecting a first resistor, the emitter to collector circuit of said second transistor and .a second resistor in series across said terminal means, means connecting the base electrode of said first transistor directly with the collector electrode of said second transistor, a voltage dividing network connected across said terminal means, and a Zener diode connected between the base electrode of said second transistor and said voltage dividing network.

References Cited by the Examiner UNITED STATES PATENTS 2,963,624 12/1960 Meyer et al 315-209 3,018,385 1/1962 OBerry 307-885 3,020,904 2/1962 Kerr 315-209 3,136,939 6/1964 Scott 323--22 X 3,138,751 6/1964 Brester 32322 X JOHN W. HUCKERT, Primary Examiner. JAMES D. KALLAM. DAVID J. GALVIN, Examiners, 

